Frequently it is desirable to provide a valve or other connection between one pipe and another pipe at a location at which the first pipe has no port or other opening at which the connection can be made.
The pipe is then drilled and a fitting, such as a valve housing or simply a connecting fitting, may be applied to the drill pipe and sealingly clamped around the hole to make the connection.
The aforementioned technique is difficult to carry out when the first pipe is under pressure and complicated devices are required for guiding the drill.
Thus it has been proposed to provide a valve housing which surmounts the pipe at the location to be provided with a valve, this housing being formed with a guide passage through which a drill can be advanced to penetrate the wall of the pipe and connect this passage to the fluid stream. The housing is also formed with a fitting for connection to another pipe and communicating with this passage, a valve member being provided between the main passage of the housing and the further passage for the control of fluid flow between the two pipes.
Reference can be had to a British Pat. No. 19,628 which discloses a valve of this type in which the valve member is a ball fixed to a control rod sealingly guided in a bushing which, in turn, is received threadedly in a sleeve. The sleeve is connected by a screw thread to the fitting or outlet-forming portion of the housing.
Upon attachment of the housing to the pipe which is to be formed with the valve or connection, the main passage is used to allow the drill to engage the wall of the pipe and bore a hole therein.
Upon formation of this hole, the drill is withdrawn and the positioning rod is actuated so that the ball enters the axial passage, i.e. the passage previously occupied by the drill and which generally extends radially of the pipe.
The ball is thus urged by the pressure of the fluid against an upper portion of the axial main passage of the housing to seal the latter against the exterior.
The drill and the guide are then replaced by a valve unit which is attached to the housing and the valve unit can include a stem which urges the ball away from the seat and thus permits pressure equalization on opposite sides of the ball. The valve can then be closed by the stem. The auxiliary blocking elements can then be removed and the auxiliary passage through which it was inserted can serve to receive the pipe to which the valve is also to be connected, i.e. the second pipe can be connected to the fitting at the latter passage.
An assembly of this type frequently has the disadvantage that the ball either does not seat fully or its displacement into full sealing relationship causes the loss of sealing action around the actuating rod. This is because the packing bushing around this rod is stressed not only axially but also radially by the pressure of the fluid against the ball.
Still another disadvantage of this earlier system is that the use of a ball requires the housing to have large dimensions corresponding to the diameter of the ball or to its thickness dimension measured radially with respect to the pipe or axially along the main or boring passage. This frequently is inconvenient and prevents use of the assembly where space is at a premium. This is especially the case when the main passage practically corresponds to the diameter of the bore to be drilled in the passage.
Reference may also be had to the system described in German Pat. DT-PS No. 855,344 which provides a housing into which a latter sleeve can be treated for sealing engagement with a spindle. This spindle can have a wedge-shaped sealing plate on its end penetrating into the housing. The sealing plate is used as a slide along carefully machined or constructed guide surfaces to block the housing passage. Naturally, the precision with which such a device must be constructed renders the assembly expensive and disadvantageous for many applications.